TELEOSTEI. 315 



they are not known to be represented by any fossil forms. 

 There remain, therefore, for consideration the orders of the 

 Teleostei (Bony Fishes), Ganoidei (Ganoids), Elasmobranchii 

 (Sharks and Rays), and Dipnoi (Mud-fishes). 



CHAPTER XXIX. 



ORDERS OF FISHES. 



ORDER I. TELEOSTEI. This order includes the great majority 

 of fishes in which there is a well-ossified endoskeleton, and it 

 corresponds very nearly with Cuvier's division of the "osse- 

 ous " fishes. The Teleostei are defined as follows : The skele- 

 ton is usually well ossified ; the cranium is provided with cranial 

 bones, and a mandible is present; whilst the -vertebral column 

 almost always consists of more or less completely ossified vertebrce. 

 The pectoral arch has a clavicle; and the two pairs of limbs, when 

 present, are in the form of fins supported by rays. The gills are 

 free, pectinated or tufted in shape, a bony gill-cover and branchio- 

 stegal rays being always developed. The branchial artery has its 

 base developed into a bulbus arteriosus ; but this is never rhythmi- 

 cally contractile, and is separated from the ventricle by no more 

 than a single row of valves. 



The scales in the Teleostean fishes are generally thin, horny, 

 flexible plates, which overlap one another, and have the " cy- 

 cloid " or " ctenoid " characters. The order, therefore, corres- 

 ponds, in a general way, with the orders Ctenoidei and Cycloidei 

 of Agassiz. Some of the Teleostean fishes, however, are pro- 

 vided with ganoid scales. 



Excluding the Leptolepidce, which are sometimes referred to 

 this order, the Teleostei do not seem to have any representatives 

 in times anterior to the Cretaceous period that is, towards the 

 close of the Mesozoic period. From this time on, however, Bony 

 Fishes with cycloid or ctenoid scales are the chief fossil repre- 

 sentatives of the whole class of the fishes, and the order 

 appears to have attained its maximum at the present day. 



The order Teleostei is divided 'into the following sub-orders : 



SUB-ORDER A. MALACOPTERI, Owen (= Physostomata, Mul- 

 ler). This sub-order is defined by usually possessing a com- 

 plete set of fins, supported by rays, all of which are " soft " or 

 many-jointed, with the occasional exception of the first rays in 

 the dorsal and pectoral fins. A swim-bladder is always present, 



